Tank Won't Fluctuate

Question

Hello,

I have a water model with multiple pressure zones. I have a pressure zone (pressure zone A) which gets its supply from a lower pressure zone. Pressure zone A has its own booster pump station with 3 identical pumps which feeds a variable area elevated tank A and then distributes to pressure zone A. When I run extended period simulations the tank HGL is a flat line over time at whatever initial water elevation I enter and 1 of the 3 booster pumps is constantly running and not shutting off. This is a model rebuild and I have tried to compare to the previous version to see why the zone works in the old version and in the new version it doesn't but I can't seem to figure out why cause most of the settings are the same. There are new pump curves at the booster station (as well as other stations), new demands throughout the model, some new piping in areas, new global multipliers, some new tanks, modified pumping controls, etc. Is there some easy way to compare the old model and the new model? I'm running out of ideas as to why the zone isn't functioning properly.

Pumps are at elevation 280.56'

Pump Curves Standard 3 point

Shutoff 0, 86.64 (Flow gpm, Head ft)
Design 155, 70.38 (Flow gpm, Head ft)
Max. Operating 239, 41.67 (Flow gpm, Head ft)

Controls

Tank A Hydraulic Grade <= 434.00 ft A P1 Pump Status = On
Tank A Hydraulic Grade <= 433.00 ft A P2 Pump Status = On
Tank A Hydraulic Grade <= 430.00 ft A P3 Pump Status = On
Tank A Hydraulic Grade >= 438.00 ft A P1 Pump Status = Off
Tank A Hydraulic Grade >= 436.00 ft A P2 Pump Status = Off
Tank A Hydraulic Grade >= 433.00 ft A P3 Pump Status = Off

300,000 gallon variable Area Elevated Tank A

Leg Support Concrete Pads Elevation 333.5'

Base Elevation 410'

Min. Elevation 410'

Max Elevation 440'

Initial Elevation 433.5'

Max Diameter 44'

Cross-Section Curve Depth Ratio % / Volume Ratio %

0.0 / 0.0
10.0 / 5.0
20.0 / 13.0
30.0 / 23.0
40.0 / 34.0
50.0 / 46.0
60.0 / 57.0
70.0 / 68.0
80.0 / 79.0
90.0 / 90.0
100.0 / 100.0

Thanks

Ryan

Yashodhan Joshi · Answer

Hello Ryan,

You say that this is a model rebuild. What do you mean by that? Was the original model prepared in an earlier version of WaterGEMS / WaterCAD? Or was it prepared in some other product?

If you have opened an old WaterGEMS / WaterCAD model in your current version then it would be simply a case of element tracking. You'd have to manually check the components and data input between the models. However, if you have the model data in GIS format (or can convert it to GIS format by exporting the element flextables), then you can try something like this.

1. Re-create the old model first in the current version of WaterGEMS / WaterCAD by importing the GIS data using ModelBuilder. Create a "snapshot" of this in ModelBuilder.

2. Now run it and see if it is running similar to how it was in the previous version.

3. Export the element flextables for the "new" model to GIS.

4. Now "update" the model using the updated GIS dataset. Since your latest model is containing additions to the old model you can see the changes between them by tracking the snapshots. See this article for details - Using ModelBuilder snapshots to help track changes and updates between source file and model file

5. This will let you know what changes are affected in the model from then till now.

Considering the changes see if there is any input which was incorrect and you can only focus on the changes as the model previously worked satisfactorily.

If you have an old model which was prepared in some other product, then you should understand how it was brought into WaterGEMS / WaterCAD. If it also has a GIS database then you can adopt the above procedure. See this article for details on importing models from external products;

Importing or Exporting to WaterCAD, WaterGEMS, HAMMER from other software

Considering your problem of the tank HGL remaining flat throughout, it may be due to the tank being in an equilibrium i.e. the inflow to the tank matches the outflow. Simply put the tank is filling and emptying at the same time. Also the controls you have setup are a bit confusing. If Pump P1 is "On" when HGL <= 434 then it could be conflicting with the other conditions too. HGL <= 434 can mean the HGL is 415 (for example) then all the pumps will operate since this condition is less then all. But once the water starts to rise, say at HGL = 431 technically this should stop the pump P3 (since HGL > 430) but the "Off" condition for the pump P3 is at (HGL >= 433).

There could be some other reasons for this also. If possible please share the model files with us to investigate this;

Sharing Hydraulic Model Files on the OpenFlows | Hydraulics & Hydrology Forum

Hope this helps.

Regards,

Yashodhan Joshi